Fructose Flashcards
Historical perspective of fructose intake
- ever increasing sugar intake
- change in the type we consuming - more HFCS
How do different sugars differ in sweetness and GI?
very sweet but low GI
Why is fructose often used in food industry?
sweeter, cheaper, good consistency
Is fructose the optimal low GI sweetener?
No, it has a different metabolic fate from glucose and contributes little to energy
metabolic fate of fructose
fructose breakdown uses ATP to make fructose 1 phosphate and process makes uric acid
* F1P can be further broken to make pyruvate with more production of urin acid or can be converted to TAG
How does F1P effect glucose?
- stimulates glycolysis
- stimulates glycogenesis and inhibits glycogenolysis
Proposed effects of fructose on hepatic lipid metabolism
- Increases TG packaged into the VLDL
- contributes to hepatic denovo lipogenesis
How fructose and glucose differ with effects on brain regions involved with appetite and reward?
fructose provokes feeding (promotes less satiety hormones) and glucose promotes greater satiety
What is the difference in metabolic and hormonal response between fructose and glucose?
Fructose drink results in a lower insulin response, lower GLP-1 response and more lactate.
* shows spill over in the 2 paths
What enzyme first breaks down fructose
fructokinase
* it is not sensed by glucokinase
Does glucose or fructose produce more satiety?
- glucose leads to greater fullness and satiety
- fructose does not lead to fullness likely due to less insulin and GLP-1 and people will often eat more
How do fructose and glucose differ in brain activation?
- more activation with glucose in the hypothalamus, thalamus, putamen, caudal
- fructose has only a small activation in the hypothalamus and thalamus
What might control sugar seeking behaviour?
glucose responsive neurons expressing GLUT2 in the paraventricular thalamus (PVN)
* may control sugar overconsumption in obesity and T2D
* Also expressed in the beta cells
What happens with loss of neuronal GLUT2?
increases glucose seeking behavior
* Eat more food wtihout GLUT2 in the brain
When are GLUT 2 expressing neurons activated?
They are activated, or make you go seek food, at kow glucose
* Once you consume glucose they are deactivated
How do GLUT 2 expressing neurons respond to fructose?
Do not respond to fructose so still activated after a fructose meal (still seeking food)
What has confirmed the role of GLUT2 neurons in glucose seeking behaviour?
Optogenetics
* a biological technique to control the activity of neurons or other cell types with light.
* increases CBF
Summary of fructose studies
First time fructose was linked with diabetes
research article 1977 - diabetes induced by a high fructose diet
How might fructose effect the gut microbiome?
Fructose has the potential to affect “gut health”, including barrier deterioration, dysbiosis, and the production of active metabolites (FA, glycerate).
* fructose can cause microbiome changes to make SCFA
* increased permability of the endothelium
* endotoxemia - microbiome and their products can enter the body
How does fructose consumption compare to an already bad diet?
glycerate from intestinal fructose metabolisms induces islet cell damage and glucose intolerance
* glycerate is toxic to islets
How does a HF diet compare to CD?
The HFD resulted in greater levels of glycerate both in the portal vein and systemic circulation
What happened with rats treated with glycerate?
rats treated with glycerate have degraded islets and impaired fasting glucose
Where is fructose metabolized?
Fructose was thought to be metabolized predominantly in the liver, but evidence is emerging that it is also metabolized in the small intestine.
